Tstl Lise M S Pta

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Concernant la présentation orale.

La durée est parfaite (5:26 mins),

Il y a quelques petites erreurs comme "answer about cocoa powder" =} "answer the question about cocoa powder", or "all of this results" =} "all these results"

Attention Ă  la prononciation de certains mots comme ""cocoa", "powder", "petri-dish", "PCA".. et Ă  l'emploi du verbe "make" ("we made an MIC, TLC"… =} "We did an MIC or "we carried out an MIC"). Attention aussi Ă  l'emploi des sujets relatifs comme who (pour une personne) et which (pour une chose/idĂ©e,..), par exemple "one who is expired" =} "one which expired", "an assessment who said" =} "an assessment which showed

Sinon, c'est très bien présenté et ton texte est bien écrit


The cocoa powder

1/Introduction and research made:

First, we had started on the subject of the alcoholic hydro gel, but another group had the idea. So we have to find another one. We were looking for something in the food-processing industry, because whatever the food is, we would have already met it, whether it is during everyday life or during a culinary discovery. We then thought of chocolate and a member of the group with expired cocoa powder put a subjection to the group, that of exploiting cocoa powder as a material for the PTA. Given that we often heard that “cocoa powder does not expire”, why would there be an expiry date on the package and what would make cocoa expired?

We wondered what could change/evolve over the shelf life of the product when it is not stored under optimal conditions.
We were able to find an assessment: cocoa powder is better preserved when it is kept in a jar made of glass or metal sealed tightly, away from light and humidity.

We asked ourselves about the composition of the cocoa to arrive at possible experiments to continue, in order to be able to highlight the probable variants between a cocoa powder expired since 2015 and a new one for the project that expired in 2021.
We were able to do microbiological and biochemical tests and observed various conclusive results. We have also met difficulties with some experiments. However, we were able to obtain pertinent results and change elements on our protocols when we needed to.

Key question: What are the consequences if we do not respect the storage conditions, ideally provided for cocoa powder?

2/ Experiments released:

To answer to this question we made a lot of hypothetical experiment and decide to do these ones:

During the 1st test session:

- A colony count in the mass on PCA (Plate Count Agar)
-A Gram staining
- The flag technique
-An isolation on TS agar medium
-A TLC (Thin-layer Liquid Chromatography)

During the 2nd test session:
-The water content
-A IMC = inhibitory minimal concentration
- A protein extraction
- 2 colorimetric analysis, one for the carbohydrates and one for the proteins.

3/The colony count in the mass on PCA (Plate Count Agar)

We did a colony count in the mass with cocoa powders to determine if there is on there is not micro-organism in each of them.
Given that the powder expired since 2015 and has been conserved in an alimentary bag made from paper in its original cardboard box. The bag never has been totally closed; maybe this powder could have micro-organism from the environment. And for the cocoa powder that will expire in 2021, the presence of micro-organism can show a hygiene problem from the method to obtain the powder.

4/Our results:

We had some disappointing results but they all give us something to use to find an answer to the key question.
We met some problems with the colony count (that’s why we made the flag technique) and during the Gram staining.

• So let’s start with the colony count in the mass on PCA medium:
We found colonies but they were on the medium and not in like they supposed to be. In the mass they were nothing, that’s means that cocoa powders don’t have micro-organism. The colonies on the top of the medium were contaminants from the lab and student who were walking around (we made the flag technique with these ones but it’s not useful).

• Because of our precedent result we thought that cocoa powder got something in its components that inhibit micro-organism. We decided to release the IMC to answer to our theory.
When we saw the results of the IMC, we observed that bacteria tested have grown on all test tubes which mean that the cocoa powder doesn’t have a component that inhibit micro-organism.

• We made the isolation on TS agar medium to confirm the fact that there is no micro-organism and the experiment confirms it.

• For the water content we found that the cocoa powder 2021 has a bigger percentage then the cocoa powder 2015.
We found this result kind of incoherent because the cocoa powder, when you have a look on it you can see the powder in form of piece which is prove of humidity for powder. We wanted to retest it but didn’t found the time.

• When we made the TLC we met a problem. The powder was to dark and the task that we observed were not correct because when we wanted to confirm the experiment with the control ones.

• To make the colorimetric analysis we had to make the protein extraction because the lipids could disturb results. So for the colorimetric analysis we observe the same results for the 2015 and 2021 powders when we did it for the carbohydrates and we had the same concordance for the proteins.


If you remember the beginning of our technical project we found an assessment who said: “cocoa powder is preserved in best conditions when it is kept in a jar made of glass or metal sealed tightly, away from light and humidity.”

When we test our powders we saw that nothing has changed between the one who is expired from 2015 and the one who is not. Our results told to us that the proteins are the same, the carbohydrates too, the content water didn’t change and the most important of them, there is not micro-organism. To finish, thanks to our experiments and ideas we can say that the cocoa powder doesn’t expired but we know this for only a powder expired during 5 years. And you can also conserve your cocoa powder in its original container.
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